Project Summary: Polarized membrane traffic is an essential feature of all eukaryotic cells, and is regulated in part by the cycle of GTP binding and hydrolysis of the small Rab GTPases. We have recently shown that the Elp protein complex, regulates polarized secretion in yeast by modulating this cycle for the Rab Sec4p in an unknown, but transcriptionally independent fashion. This is a novel finding as the regulation was dependent on an acetyltransferase (AT) activity present in the complex. The most conserved protein of the six-subunit Elp complex is ElpSp, which contains the AT domain as well as an S-Adenosyl Methionine (SAM) radical domain. The substrates of these activities are unknown, necessitating fundamental research into their identities and nature. This research proposal focuses on the enzymatic activities of ElpSp with a combination of biochemical and genetic analysis. The major goals are to identify the acetylated targets, establish the consequences of this modification, identify the deacetylase(s) that reverses the modification, and elucidation of the substrates and chemical reaction catalyzed by the SAM radical domain. This work is of fundamental importance to understanding the role the Elp complex plays in secretion regulation. Relevance: Mutations of a human homolog of an Elp complex protein underlie the human neurodegenerative disease, Familial Dysautonomia. The biological process this mutation affects is not understood and no animal models exist to study it. The homologous complex from yeast offers an exciting opportunity to gain insight into this devastating disease. Moreover, this proposal focuses on the cytoplasmic acetylation caused by the Elp complex, a protein modification with relevance to anti-cancer therapies under development. [unreadable] [unreadable] [unreadable]